An operation detection device 2 as shown in FIG. 8 will be described as a generally employed sensor fixation device. The operation detection device 2 includes an operation state detection sensor 3 that abuts on a steam trap inlet 1 as a detection object, a retaining member 4 connected to the operation state detection sensor 3, having a pair of insertion holes, which is positioned on one surface of the steam trap inlet 1, a grip member 5 which is positioned at the opposite surface of the steam trap inlet 1, formed substantially in a channel shape in cross section having an upper wall and both side walls, and having a pair of insertion holes in the upper wall, a plane part which is formed between the pair of the insertion holes, contacts with the plane part of a square pillar of the detecting portion and grooves of substantially V-shape in cross section that are formed on both side walls, and contacts with both sides of the curved surface of a round pillar of the detecting portion, a U bolt 6 having both legs 6a inserted into the pair of insertion holes of the grip member 5 and the retaining member 4, and a pair of nuts screwed to both legs 6a of the U bolt 6 (see Patent Literature 1).